Nitrogen oxide (NOx) in a flue gas discharged from an electric generation plant, a car, and others is a material that can cause urban ozone and acid rain. The most practically advanced selective catalytic reduction method in technologies that decompose NOx in the flue gas into harmless nitrogen (N2) and water (H2O) uses ammonia (NH3) as a reducing agent and allows NH3 to react with NOx in the flue gas in the presence of a denitrification catalyst.
NOx removal efficiency required for a flue gas denitrification apparatus 3 (see FIG. 9) installed in a thermal power generation boiler is calculated based on the following computational expression:NOx removal efficiency=((inlet NOx concentration−outlet NOx concentration)/(inlet NOx concentration))×100%
To achieve the NOx removal efficiency calculated based on the computational expression, the flue gas denitrification apparatus 3 is loaded with each catalyst block 1 in which a plurality of catalyst units 2 as a minimum unit are incorporated, and the catalyst block 1 is supported by support beams 14 in the denitrification apparatus 3 (a reactor). It is to be noted that the catalyst unit 2 is formed by laminating catalyzers each having a catalyst applied to a substrate surface at fixed intervals and accommodating them in a frame.
In general, an exhaust gas temperature in the flue gas denitrification apparatus is as high as approximately 300 to 400° C., and a large amount of smoke dust of approximately 10 to 20 g/m3N is contained. The exhaust gas containing NOx flows into the denitrification apparatus 3 from a boiler outlet and is purified by a denitrification reaction in the presence of ammonia when it passes through the catalyst block 1, but denitrification performance is considerably deteriorated by catalytic cogging when ash or the like is accumulated on the catalyst block 1. Therefore, many catalyst blocks 1 are arranged in a frame body 13 shown in FIG. 10, each angle steel 18 (shown in FIG. 11 which is an enlarged view of a circular frame S1) or each round steel 19 (shown in FIG. 12 which is an enlarged view of a circular frame S2) is arranged in a gap between the adjacent catalyst blocks 1, 1, and each angle steel 18 or each round steel 19 is welded and fixed to the frame body 13 on site where the flue gas denitrification apparatus 3 is installed, thereby avoiding deposition of the ash.
As known literatures, there are the following Patent Documents 1 and 2. In particular, as an invention described in Patent Document 2, there is disclosed a configuration that a dust attachment preventing protective equipment of angle steel is disposed on the gas upstream side between adjacent cases of catalyst unit cases arranged in a flue gas denitrification apparatus 3 and the protective equipment preventing attachment of dust is disposed between a gap between catalyst units adjacent to each other and an inner wall of the denitrification apparatus 3.